B How do we know that light that comes from the stars is in past?

5
0
So for some reason, from time to time, i always come back to this question and i can't remember that part of the physics while i was studying and most of the explanation are pretty generic.

Basically how do we know that light actually travels and not just oscillate and transfer energy when continuous flow is established between source and observer ?
 

russ_watters

Mentor
18,849
5,040
So for some reason, from time to time, i always come back to this question and i can't remember that part of the physics while i was studying and most of the explanation are pretty generic.

Basically how do we know that light actually travels and not just oscillate and transfer energy when continuous flow is established between source and observer ?
Well, we know that light travels at a finite speed, right?
 
5
0
Well, we know that light travels at a finite speed, right?
Yeah, and that is fine and completely understandable. But if continuous flow is established between light source and observer, how can we prove that what we actually see is single particle that has traveled from point A to point B, and not just oscillation which transfers energy (something similar to AC current)?
 

russ_watters

Mentor
18,849
5,040
Yeah, and that is fine and completely understandable. But if continuous flow is established between light source and observer, how can we prove that what we actually see is single particle that has traveled from point A to point B, and not just oscillation which transfers energy (something similar to AC current)?
What you are saying in that last bit really doesn't make any stand-alone sense at all (AC current travels at almost the speed of light too). But taken as a whole, since we have a well established understanding of how light works on earth and in our solar system, there is no reason - no evidence - to believe some totally unrelated process is at work at longer distances.
 

phinds

Science Advisor
Insights Author
Gold Member
15,396
5,038
Basically how do we know that light actually travels and not just oscillate and transfer energy when continuous flow is established between source and observer ?
I don't see how that could possibly account for red-shift that varies with distance, just to name one issue.
 
93
16
Basically how do we know that light actually travels and not just oscillate and transfer energy when continuous flow is established between source and observer ?
Experiments with light have been made between the Earth and the Moon. In fact, mirrors have been mounted on the Moon, to send a beam from the Earth, reflect it on the Moon and receive it again on Earth. Those two and a half seconds of round trip have been well proven in those experiments. Any astronomical distance can be considered as a series of stretches, all in the order of the distance between Earth and Moon. If everyone behaves like the space between Earth and Moon, then the time differences estimated by astronomers can not be too wrong. Within the instrumental possibilities, they must be perfectly valid.
 
28,310
4,659
Basically how do we know that light actually travels and not just oscillate and transfer energy when continuous flow is established between source and observer ?
Because Maxwell’s equations say it does and we have lots of evidence that light obeys Maxwell’s equations.
 

Want to reply to this thread?

"How do we know that light that comes from the stars is in past?" You must log in or register to reply here.

Related Threads for: How do we know that light that comes from the stars is in past?

Replies
6
Views
4K
Replies
1
Views
2K
Replies
4
Views
2K
Replies
29
Views
5K
Replies
42
Views
2K
Replies
3
Views
3K
Replies
8
Views
2K
Replies
5
Views
835

Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving
Top